Paper sized with linear cationic polymer



United States Patent Yun Jen, Anaheim,

The present invention relates to the manufacture of paper of improved water resistance sized by a content of a normally water-soluble linear carbon chain vinyl polymer, as more particularly described below. The invention particularly relates to sized paper of the type described having comparatively high dry strength, wherein the polymer acts in addition as bonding agent for the fibers.

It is known that paper of improved resistance to penetration by water may be prepared by adding certain watersoluble cationic polymers containing non-ionic hydrophobic groups and cationic hydrophilic groups to aqueous suspensions of papermaking cellulosic fibers, whereby the polymeric material is substantively adsorbed by the fibers, sheeting the fibers to form a wet web, and drying the web. However, it is a principal disadvantage that the paper thus manufactured has a decreased dry strength, as compared with paper prepared in the same way from untreated fibers. Evidently the sizing agents interfere with the normal fiber-to-fiber bonding which normally occurs when the fiber are sheeted from aqueous suspension and the wet webs thus obtained are dried.

The discovery has now been made that paper having satisfactory sizing and substantially improved dry strength can be prepared by contacting cellulose fibers with an aqueous solution of a cationic polymer as hereinafter described and heating the fibers to dry the same and develop the water-resistant properties of the polymer thereon. The polymer is substantially composed of linkages, CHXCX(C H.,CH Cl)- linkages, and quaternary ammonium linkages formed by reaction of a water-soluble tertiary amine with linkages, the number of being between about 2% linkages in the polymer.

In addition to being well sized, the paper produced by the process, in preferred embodiments, possesses the following advantages:

(l) The dry strength of the paper is substantially improved with little or no improvement in wet strength,

(2) The paper may have a nearly neutral or even an alkaline pH. It may thus contain acid-sensitive dyes, pigments and fillers.

(3) The sizing is resistant to alkali. As a result, the paper can be used for the packaging of materials such as lime, cement and soap.

In the process, heating the paper in the range of 150- 250 F. is necessary to develop the Water-repellent properties of the size of the fibers. From chemical theory no reaction of the applied sizing agent with the cellulose of the fibers appears possible in the brief heating which takes place during drying, and accordingly it has not been possible to identify the precise structural features which cause the sizing effect.

From the foregoing it will be seen that the product of the present invention is paper composed of waterlaid cellulose fibers sized by a small amount, generally between 0.05% and 3% based on the dry weight thereof of the polymer referred to.

The paper of the present invention may be made both quaternary ammonium linkages and 20% of the total number of by the tub and by the beater-addition processes. In both methods cellulose fibers are contacted with the polymer in the form of a dilute aqueous solution, and a predeter mined, effective amount is employed so that the amount in the final paper is within the range stated. In the tub method, the amount of solution picked up or adsorbed by the paper is generally about the same as its dry weight, so that the concentration of polymer in the solution i between about 0.05 and 3.0% of the dry weight of the fibers. In the beater-addition method the pH of the suspension on addition of the polymer solution is between 4.5 and 8, and the polymer is substantively and substantially completely adsorbed by the fibers. The precise amount of sizing agent employed in any instance depends on the amount of sizing desired, and this is readily deter, mined by laboratory trial as shown in the examples below.

The paper of the present invention possesses negligible wet strength. The paper therefore can be repulped in ordinary beater equipment without requiring disintegration treatment with steam jets or chemicals.

In the polymers described above, linkages and [CHX(C H CH CD] are hydrophobic and the invention does not depend on the ratio between the groups. The quaternary ammonium linkage is hydrophilic and water solubilizing. The proportion of quaternary ammonium linkages present is at least sufiicient to render the polymer water-soluble, but the proportion should not be so high as to make the polymer a a whole hydrophilic. The presence of too high a proportion of quaternary ammonium groups can easily be recognized by casting a film of the polymer and noting whether the film is or is not wet by water. If the film can be wet, the polymer contains too many quaternary ammonium groups.

As a practical matter we find that at least about 1%- 2% of the total number of linkages in the polymer should be of the quaternary ammonium type. At least this proportion is needed to render the polymeric molecule sufliciently soluble for use in an aqueous system. However, with such a small proportion of quaternary ammonium groups present the polymer is very feebly cationic and is therefore best employed by the tub method. The cationic strength of the polymer increases rapidly as the proportion of quaternary ammonium groups raised, and the polymer as a whole become strongly cationic when the number of linkages containing such groups is between about 10% and 15% of the total number of linkage in the macromolecule. As a result polymers containing this pro portion of quaternary ammonium groups are suitable for employment in the beater-addition process wherein the polymer is added-as an aqueous solution to a dilute aqueous suspension of papermaking fibers, and the polymer is substantively adsorbed by the fibers while they are in aqueous suspension. In that range the number of hydrophobic groups remains sufficiently high that the molecule as a whole is strongly hydrophobic resulting in development of paper of very satisfactory water resistance.

Polymers wherein more than about 20% of the linkages are quaternary ammonium as described are water soluble and strongly cationic. However, they are hydrophilic as well, and consequently result in development of paper of comparatively poor water resistant characteristics.

The invention does not depend upon the particular method employed for the synthesis of the polymers, and any uitable method may be employed. In general, we find it most convenient to prepare such polymers by dissolving a poly-ar-methyl styrene in a suitable solvent such as chloro-alkane and to chlorinate the polymer so as to convert at least about 2% of the ar-methyl groups therein into archloromethyl groups. The polymer at this point is substantially composed of -CHXCX(C H CH and -CHXCX(C H CH Cl) linkages, wherein X represents hydrogen or chlorine. The polymer is then quaternized with at least sufiicient of a water-soluble tertiary amine to render the macromolecule water soluble (and if desired cationic) without rendering the whole molecule hydrophilic as explained above. With one typical tertiary amine the following is the theoretical equation for the reaction:

Suitable tertiary amines include trimethylamine, trimethylamine, triethylamine and pyridine.

The polymers may also be prepared by homopolymerizing chloromethyl styrene or a mixture of methylstyrene and chloromethyl styrene, followed by subjecting the polymer to quaternization as described. It will be understood that the polymer need only be substantially composed of the linkages specified above and that polymers containing minor amounts of one or more diluent linkages are within the scope of the present invention.

The invention will be more particularly described with respect to the examples which follow. These examples are specific embodiments of the invention and are not to be construed as limitation thereon.

Example 1 The following illustrates the preparation of sized paper according to the present invention.

10 gm. of commercial polymethylstyrene (approximately 65% p-methylstyrene, 33% o-methylstyrene and 2% m-methylstyrene) was dissolved in carbon tetrachloride and chlorine bubbled into the solution at moderate rate under sunlamp irradiation until about one mol equivalent of C1 had been charged. The product weighed 12.7 gm. Of this, 10.0 gm. was dissolved in a 90 gm. dioxane- 100 gm. butyl cellosolve solution and heated for 145 minutes at 97 C. with 4.0 gm. of pyridine. The product was used as a 2.5% solution in water.

Aliquots were taken from a bleached 50:50 sulfitezhardwood kraft pulp at 0.6% consistency beaten to a Green greeness of 450 ml., and to these were added polymer in amounts shown in the table below. The pH value were adjusted as indicated, and after a few minutes of stirring the aliquots were sheeted at 45-50 lb. and at 200 1b. basis weight (25" x 40"/ 500 ream). The sheets were dried for 1 minute at 240 F. on a laboratory drum drier and tested Results are as follows.

by TAPPI methods.

Percent Sizing Lactic Dry Burst Run Polymer Pulp Currier Acid No. Added 1 pH (Sec.) 7 Resist.

(Sec.) 3 (Lb/in.) 4 Percent None 7.0 0 17 0.5 8.0 34 15 19 12 0.6 8.0 105 0.75 8.0 40 545 22 29 1.0 8.0 45 1,80O 23 35 1.0 6.0 43 1,8 23 35 2. 0 8. 0 42 1, 800 21 24 1 Based on dry weight of fibers.

Slack scale.

8 By penescope, using 20% aqueous lactic acid at 100 F. I Mullen.

The results show that the polymer imparted considerable sizing while actually improving the dry strength of the sheet.

Example 2 Weight) was precipitated in methanol and reprecipitatcd from methyl ethyl ketone and was dissolved in 859 gm. of methyl ethyl ketone. To the solution 41.0 gm. of pyridine was added. The mixture was reacted at reflux (79 C.) and samples were withdrawn every 30 minutes. The samples were immediately diluted with water to 2% solids content and the ionizable chloride content titrated potentiometrically with 0.1 N AgNO using a silver electrode and dilute HNO to adjust acidity, and the number of quaternary ammonium groups determined as a percentage of the total number of combined styrene (including substituted styrene groups) present. The samples were then tested for their sizing value by the method of Example 1, the amount of polymer added being in each instance 0.5%

of the dry weight of the fibers. Results were as follows.

Reaction Percent Polymer Sizing Tensile Sample No. Time, Quat. Soly. in Currier 1 Strength,

Mins. H20 (Sec.) LbJln.

1 Percent quaternary ammonium groups based on total number of styrene (including substituted styrene) linkages.

1 Slack scale.

Mullen.

Example 3 The following illustrates the preparation of sized paper according to the present invention using the tub method. For this a non-cationic polymer (polymer No. 1 of Example 2) was used.

The bath was formed by diluting the sample to 0.05 polymer content and adjusting the pH of the bath to 8. Sheets of 50:50 bleached sulfitezbleached hardwood kraft raw paper were impregnated with the solution and drum dried for 1 minute at 240 F. The paper had an estimated polymer content of 0.05% and gave a Currier value of 74 sec.

Thees results, taken with the results of Example 2, show that conversion of at least about 1%2% of the total number of styrene groups (including substituted styrene groups) to quaternary ammonium form is necessary for development of a tube size and that conversion of about 5% of the groups to quaternary form is necessary for development of a size useful as a beater additive. The results further show that when more than about 20% of the groups are quaternized, the polymer becomes so hydrophilic that it loses most if not all of its sizing value.

Example 4 The following illustrates the results'obtained with polymers prepared by the use of various tertiary amines as quarternizing agents.

The procedure of Example 1 was followed except that the following tertiary amines were used in place of the pyridine: trimethylamine, lauramidopropyl dimethylamine, dimethyl octadecylamine, dimethyl dodecylamine, and 2-picoline. In each instance sufficient amine was reacted to form 12%-15% quaternary ammonium groups based on the total number of styrene (including substituted styrene) linkages present. The resulting polymers were water-soluble and were tested by the beateraddition method of Example 1, 0.75% of polymer being added based on the dry weight of the fibers. The handsheets were satisfactorily sized and had improved dry strength as compared with the untreated controls.

linkages, CHXCX(C H CH CI) linkages, and quaternary ammonium linkages formed by reaction of CHXCX(C H CH CI) linkages with a watersoluble tertiary amine, wherein X designates a substituent from the group consisting of hydrogen and chlorine, the number of said quaternary ammonium linkages being between about 2% and 20% of the total number of linkages in the polymer.

2. Paper composed of waterlaid cellulose fibers sized by a content between 0.05% and 3%, based on the dry Weight of the fibers, of a normally Water-soluble cationic vinyl polymer substantially composed of linkages, CHXCX(C H CH Cl) linkages, and quaternary ammonium linkages formed by reaction of CHXCX(C H CH CI) linkages with a watersoluble tertiary amine, wherein X designates a substituent from the group consisting of hydrogen and chlorine, the number of said quaternary ammonium linkages being between about 10% and of the total number of linkages in the polymer.

3. A process for the manufacture of sized paper which comprises contacting cellulose fibers with an aqueous solution of a vinyl polymer substantially composed of -CHXCX(C H CH linkages,

linkages, and quarternary ammonium linkages formed by reaction of -CHXCX(C H CH CI)- linkages with a water-soluble tertiary amine, wherein X designates a substituent from the group consisting of hydrogen and chlorine, the number of said quaternary ammonium linkages being between about 2% and of the total number of linkages in the polymer, thereby depositing between about 0.05% and 3% of said polymer on said fibers, based on the dry weight thereof, and heating the fibers at 190 F.-250 F. to dry the same and develop the water-resistant properties of the polymer thereon.

4. A process for the manufacture of sized paper which comprises forming a dilute aqueous suspension of cellulose papermaking fizers, adding thereto from about 6 0.05% to 3%, based on the dry Weight of the fibers, of an aqueous solution of a cationic vinyl polymer substantially composed of CHXCX(C H CH linkages, CHX-CX(C H CH CI) linkages, and quaternary ammonium linkages formed by reaction of linkages with a water-soluble tertiary amine, wherein X designates a substituent from the group consisting of hydrogen and chlorine, the number of said quaternary ammonium linkages being between about 10% and 15 of the total number of linkages in the polymer, whereby said polymer is substantively adsorbed by said fibers, sheeting said fibers to form a waterlaid web, and heating said web at -250 F. to dry the same and develop the sizing properties of the polymer thereon.

5. A process according to claim 4 wherein the pH of the suspension on addition of the polymer solution is between 4.5 and 8.

6. A process for manufacturing sized paper which comprises forming a dilute aqueous suspension of cellulose papermaking fibers, adding thereto an aqueous solution containing about 0.1% to 3% based on the dry weight of the fibers of the material prepared by homopolymerizing an ar-methylstyrene, chlorinating between about 10% and 15% of the ar-methyl groups in the polymer thus obtained, and quaternizing the resulting chlorinated polymer with at least about the minimum effective amount as solubilizing agent therefor of a watersoluble tertiary amine, sheeting said fibers to form a waterlaid web, and heating said web at 190 F.250 F. to dry the same and develop the sizing properties of the polymer therein.

7. A process according to claim 6 wherein the armethylstyrene is p-methylstyrene.

8. A process according to claim 6 wherein the tertiary amine is pyridine.

References Cited in the file of this patent UNITED STATES PATENTS 2,654,729 Price Oct. 6, 1953 2,694,702 Jones Nov. 16, 1954 2,823,201 Wheaton Feb. 11, 1958 2,884,057 Wilson et a1. Apr. 28, 1959 2,884,058 Schuller et a1. Apr. 28, 1959 OTHER REFERENCES Casey: Pulp and Paper, vol. 1, 1952, Interscience Publishers, Inc., New York, page 491.

Patent N00 3 Ol5 O5 January 2 1962 Yun en ct ale It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected be1o* Column 3; lines 141 and 15 strike cut 'trimethylaminc" 9 second occurrence; line 441 for greenees read freeness column 4 line 47 for Thees read These line 51 for "153cc" read tub -====g column 55 line 50 for "fizers read fibers Signed and sealed this 27th day of November 1962,

(SEAL) Attest:

ERNEST w. SWIDER DAVID L. LADD I Attesting Officer Commissioner of Patents 

1. PAPER COMPOSED OF WATERLAID CELLULOSE FIBERS SIZED BY A CONTENT BETWEEN 0.05% AND 3%, BASED ON THE DRY WEIGHT OF THE FIBERS, OF A NORMALLY WATER-SOLUBLE CATIONIC VINYL POLYMER SUBSTANTIALLY COMPOSED OF 